In the field of agriculture and forestry and in the building and transport industries, steel ropes are usually used as hauling ropes, carrying ropes and the like for rope devices, e.g., rope pole devices or winches.
High demands are made on ropes in this application area particularly with regard to their tensile strength and their abrasion resistance, since the ropes are guided, for example, on forest soil and over tree trunks.
What is also desirable is easy determinability of the replacement state of wear, i.e., of the point in time when the rope has to be replaced as a preventive measure because of too much damage sustained in the ongoing operation.
For the above reasons, mainly steel ropes are currently used for said purposes, as already mentioned initially, since, on the one hand, they exhibit high tensile strength and, on the other hand, they are also highly resistant to abrasion.
However, the disadvantage of steel ropes is their large weight. This is disadvantageous in particular when ropes must be retracted manually, for example, for mounting tower yarders.
Therefore, attempts have already been made to use ropes made of a textile fibre material in the field of agriculture and forestry. Sheathless ropes made of a high-strength textile fibre material (e.g., of Dyneema® fibres, a high-strength and high-modulus polyethylene (HMPE) fibre material) are known.
If, however, a rope made of a textile fibre material is supposed to achieve equally high tensile strengths like a steel rope, the individual fibres have to be oriented in the rope direction to the largest possible extent, i.e., twines and cords, respectively, with a small twist and a large length of lay, respectively, have to be used. This, however, happens at the expense of abrasion resistance. In addition, it is difficult to determine the replacement state of wear of such ropes.
It is the object of the present invention to provide a rope made of a textile fibre material which is particularly suitable for use in rope devices of all kinds, especially winches, and does not exhibit the above-mentioned disadvantages.
Said object is achieved by a rope made of a textile fibre material and present in the form of a core-sheath structure in a manner known per se, which rope is characterized in that the specific strength of the rope Fs (in [daN/g core/m rope]) complies with the following formula depending on the diameter of the rope DM (in [mm]):Fs≧212−DM.
Ropes made of a textile fibre material which are present in the form of a core-sheath structure are known per se. Such a rope is made up of one or several, e.g., braided or beaten core(s) of a textile fibre material, with a textile fibre material being wrapped, e.g., braided, around said core(s) as a sheath.
For the purposes of the present invention, the term “core” denotes hereafter both a single core and a plurality of cores present in a rope.
Ropes having a core-sheath structure are indeed commonly used in many areas such as, e.g., in the field of mountaineering or nautics, but so far have not been suggested for the sector of rope devices in agriculture and forestry. This is due to various reasons:
For one thing, substantially higher tensile loads are effective in the present field of application, which tensile loads have to be transmitted to the core via the sheath. Even minor displacements between the core and the sheath will lead to poor force transmission and to the sheath being slid open. The rope will thus become susceptible to abrasion and, in addition, will exhibit a lump at the respective spot, which lump will be put under even greater stress. All this will eventually result in the destruction of the rope.